Outlook of the world steel cycle based on the stock and flow dynamics

Modeling the impact of nickel recycling from batteries on nickel demand during vehicle electrification in China from 2010 to 2050

China is promoting the production and use of electric vehicles (EVs) to achieve carbon neutrality. However, the shift will drive higher demand and tighter supply of nickel in China. We develop a stock-driven bottom-up dynamic substance flow analysis (SFA) model to simulate the demand trends of various EVs under 3 scenarios, the flow of nickel under 9 scenarios and the amount of recoverable nickel under 27 scenarios in China's EV industry from 2010 to 2050. The results indicate that China's current production capacity and primary reserves of nickel cannot meet the growing nickel demand, especially under the High EVs-LNCT scenarios, and closed-loop nickel recovery from EV batteries can effectively alleviate the demand-supply contradiction. In different scenarios, the annual recycling nickel could cover between 67.7 % and 96.6 % of the demand for EV batteries in 2050, and between 37.9 % and 58.1 % in terms of the cumulative quantity by 2050. When the low nickel battery technology is adopted and the recovery efficiency is rapidly improved, the recovered nickel would meet the demand for EV batteries to the highest degree. Therefore, sufficient attention should be paid to low-nickel battery technology and efficient recycling of spent EV batteries, which is of great significance to ensure the development of EV industry and the availability of nickel in China.

Metal Requirements for Building Electrical Grid Systems of Global Wind Power and Utility-Scale Solar Photovoltaic until 2050

Wind and solar photovoltaic (PV) power form vital parts of the energy transition toward renewable energy systems. The rapid development of these two renewables represents an enormous infrastructure construction task including both power generation and its associated electrical grid systems, which will generate demand for metal resources. However, most research on material demands has focused on their power generation systems (wind turbines and PV panels), and few have studied the associated electrical grid systems. Here, we estimate the global metal demands for electrical grid systems associated with wind and utility-scale PV power by 2050, using dynamic material flow analysis based on International Energy Agency's energy scenarios and the typical engineering parameters of transmission grids. Results show that the associated electrical grids require large quantities of metals: 27-81 Mt of copper cumulatively, followed by 20-67 Mt of steel and 11-31 Mt of aluminum. Electrical grids built for solar PV have the largest metal demand, followed by offshore and onshore wind. Power cables are the most metal-consuming electrical components compared to substations and transformers. We also discuss the decommissioning issue of electrical grids and their recovery potential. This study would deepen the understanding of the nexus between renewable energy, grid infrastructure, and metal resources.

Analysis of iron composite flow in China

Iron is an important metal material that is crucial to social and national economic development. In order to understand iron's material flow, energy flow, and value flow in China, a composite flow framework is here established. Based on this framework, the concept of price is introduced, and China is taken as an example to study the composite flow of iron in 2018. The results showed the following. First, as iron moved down the industrial chain, its material flow decreased gradually, while the price continued to rise. Second, the annual loss of raw materials from iron processing was 150-200 million tons, and scrap iron had great potential for secondary utilization. Third, China had a trade deficit in terms of importing raw materials and exporting products, but it also had a trade surplus in trade volume. Finally, China imported iron-containing goods at high prices but exported iron-containing goods at low prices. This was due to the lack of high-end science and technology, which made China less competitive in the international market.

Greenhouse Gas Emissions in the Industrial Processes and Product Use Sector of Saudi Arabia—An Emerging Challenge

The Kingdom of Saudi Arabia has been experiencing consistent growth in industrial processes and product use (IPPU). The IPPU’s emission has been following an increasing trend. This study investigated time-series and cross-sectional analyses of the IPPU sector. Petrochemical, iron and steel, and cement production are the leading source categories in the Kingdom. In recent years, aluminum, zinc, and titanium dioxide production industries were established. During the last ten years, a significant growth was observed in steel, ethylene, direct reduce iron (DRI), and cement production. The growth of this sector depends on many factors, including domestic and international demand, socioeconomic conditions, and the availability of feedstock. The emissions from IPPU without considering energy use was 78 million tons of CO2 equivalent (CO2eq) in 2020, and the cement industry was the highest emitter (35.5%), followed by petrochemical (32.3%) and iron and steel industries (16.8%). A scenario-based projection analysis was performed to estimate the range of emissions for the years up to 2050. The results show that the total emissions could reach between 199 and 426 million tons of CO2eq in 2050. The Kingdom has started initiatives that mainly focus on climate change adaptation and economic divergence with mitigation co-benefits. In general, the focus of such initiatives is the energy sector. However, the timely accomplishment of the Saudi Vision 2030 and Saudi Green Initiative will affect mitigation scenarios significantly, including in the IPPU sector. The mitigation opportunities for this sector include (i) energy efficiency, (ii) emissions efficiency, (iii) material efficiency, (iv) the re-use of materials and recycling of products, (v) intensive and longer use of products, and (vi) demand management. The results of this study will support the Kingdom in developing an appropriate climate change mitigation roadmap.

Compilation of an economy-wide material flow database for 14 stock-building materials in 177 countries from 1900 to 2016

International datasets on economy-wide material flows currently fail to comprehensively cover the quantitatively most important materials and countries, to provide centennial coverage and to differentiate between processing stages. These data gaps hamper research and policy on resource use. Herein, we present and document the data processing and compilation procedures applied to develop a novel economy-wide database of primary stock-building material flows systematically covering 177 countries from 1900- 2016. The main methodological novelty is the consistent integration of material flow accounting and analysis principles and thereby addresses limitations in terms of transparency, data quality and uncertainty treatment. The database systematically discerns four processing stages from raw materials extraction, to processing of raw and semi-finished products, to manufacturing of stock-building materials. Included materials are concrete, asphalt, bricks, timber products, paper, iron & steel, aluminium, copper, lead, zinc, other metals, plastics, container and flat glass. The database is compiled using international and national data sources, using a transparent and consistent 10-step procedure, as well as a systematic uncertainty assessment. Apart from a detailed documentation of the data compilation, validations of the database using data from previous studies and additional uncertainty estimates are presented.

• Systematically compiled historical database of primary stock-building material flows for 177 countries.

• Consistent integration of economy-wide material flow accounting and detailed material flow analysis principles.

• Methodological enhancements in terms of transparency, data quality and uncertainty treatment.

Fabrication and Characterization of Ni60A Alloy Coating on Copper Pipe by Plasma Cladding with Induction Heating

Plasma cladding coupled induction heating was developed and successfully used to fabricate Ni60A coating on the surface of copper pipe. By matching the swing arc with the rotating copper pipe, the cladding efficiency was as high as 32.72 mm2/s. From the head to the tail of the coating, the wear resistance changed from 4.5 to 1.8 times that of pure copper. During the cladding process with constant current, the surface temperature of the cladding zone and the bath depth gradually increased. The corresponding dilution ratio increased, accompanied by the widening of the interface transition zone and the growth of precipitated phases (CrB and Cr23C6). Due to the gradient change of composition, the coating can be regarded as an in situ synthesized gradient coating. The critical point of sudden change of temperature in cladding zone was 850 °C, at which point the wear mechanism changed from abrasive wear to adhesive wear. The proper surface temperature of cladding zone should be controlled within 600–850 °C, which can be achieved by matching the cladding current and induction heating power. Results indicated that plasma cladding coupled induction heating is a potentially effective method to prepare high-quality coating on the surface of a large-complex-curved copper component.

Reducing CO2 Emissions from U.S. Steel Consumption by 70% by 2050

The steel sector emits 25% of global industrial greenhouse gases, and the U.S. is the world's second-largest steel consumer. In this article, we determine how CO₂ emissions attributable to U.S. steel consumption can be cut by 70% by 2050. We vary four key steel cycle parameters (U.S. steel stocks per capita, recycling rate, product lifespan, and manufacturing yield) in a dynamic material flow analysis to determine a range of values for annual steel demand and the scrap available for recycling. We combine these data with steelmaking technology and trade scenarios to calculate potential U.S. steel sector emissions in each year to 2050. Only 20% of the pathways we modeled for the U.S. steel sector achieved the emissions target. Emissions in 2050 are most sensitive to the CO₂ released per kilogram of steel produced and the steel stocks per capita. Deployment of emerging low carbon steelmaking technology alone is insufficient to achieve the emissions cut; conversely, reducing stocks per capita from the current ∼11 tons/capita toward levels in the U.K. and France, ∼8 tons/capita, would enable the emissions cut to be achieved under a range of foreseeable steelmaking technology scenarios and steel cycle parameters. If action to reduce per capita steel stocks is delayed by more than five years, then it is likely infeasible for the U.S. steel sector to stay within its 2050 CO₂ budget because of the increased demand for emissions-intensive steel made from iron ore.

Quantifying China's iron in-use stock and its driving factors analysis

China is experiencing unprecedented industrialization and urbanization which promotes the rapid growth of iron resource consumption and in-use stock. The material flow analysis (MFA) model and the average use life method were applied to analyze China's iron in-use stock (IIUS), and the IIUS reached 7.07 billion tons in 2016 in the reference scenario. Three driving factors of the intensity of IIUS were analyzed. Among them, the per capita IIUS was rising, and it was 5.11 t/cap in 2016 in the reference scenario. In addition, the per capita crude steel output has stabilized, which was 0.58 t/cap in 2016. The intensity of crude steel use was declining and showed the inverted U-shape. The decoupling indicator was applied to analyze the relationship between IIUS and economic growth. The decoupling of IIUS from economic growth was later than that of actual iron consumption, and the IIUS did not decoupling from economic growth in recent years. The actual iron consumption has continued to decoupling from economic growth since 2010, and the decoupling indicator peaked at 1.76 in 2015. The future per capita IIUS was predicted in different scenario and the relationship between future IIUS and GDP was analyzed. The per capita IIUS will reach saturation in 2030-2040, and the intensity of IIUS also conforms to the inverted U-shape.

Cobalt in end-of-life products in the EU, where does it end up? - The MaTrace approach

The use of cobalt has experienced a strong growth in the last decades. Due to its high economic importance and high supply risk, it has been classified as a critical raw material for the EU and other economies. Part of the EU's strategy is intended to secure its availability, through fostering its efficient use and recycling. The latter is affected by factors such as the amount of available end-of-life products, and their collection-to-recycling rate. A novel methodology to analyze the impact of these factors on the cobalt flows in society is the model MaTrace, which can track the fate of materials over time and across products. The MaTrace model was expanded, adapted, and applied to predict the fate of cobalt embedded in finished products in use in the EU, considering the underlying life cycle phases within the technosphere. Eleven scenarios were built, assessing different options in the implementation of relevant EU's policies. The flows were projected for a period of 25 years, starting in 2015. The results of the baseline scenario show that after 25 years, around 8% of the initial stock of cobalt stays in use, 3% is being hoarded by users, 28% has been exported, and 61% has been lost. The main contributors to the losses of the system are the non-selective collection of end-of-life products, and the export of end-of-life products, recycled cobalt and final products. The results of the scenarios show that higher collection-to-recycling rates and lower export could increase up to 50% the cobalt that stays in use.

Material Flow Analysis with Multiple Material Characteristics to Assess the Potential for Flat Steel Prompt Scrap Prevention and Diversion without Remelting

Thirty-two percent of the liquid metal used to make flat steel products in Europe does not end up in a final product. Sixty percent of this material is instead scrapped during manufacturing and the remainder during fabrication of finished steel products. Although this scrap is collected and recycled, remelting this scrap requires approximately 2 MWh/t, but some of this material could instead be diverted for use in other applications without remelting. However, this diversion depends not just on the mass of scrapped steel but also on its material characteristics. To enhance our understanding of the potential for such scrap diversion, this paper presents a novel material flow analysis of flat steel produced in Europe in 2013. This analysis considers the flow of steel characterized not only by mass but, for the first time, also by grade, thickness, and coating. The results show that thin-gauge galvanized drawing steel is the most commonly demanded steel grade across the industry, and most scrap of this grade is generated by the automotive industry. There are thus potential opportunities for preventing and diverting scrap of this grade. We discuss the role of the geometric compatibility of parts and propose tessellating blanks for various car manufacturers in the same coil of steel to increase the utilization rates of steel.

Integrating Circular Economy Strategies with Low-Carbon Scenarios: Lithium Use in Electric Vehicles

Electrification of the transport sector will support its decarbonization, yet significantly change material requirements. This calls for an integrated modeling approach internalizing metal demand-supply dynamics in low-carbon scenarios to support the Paris agreement on climate change and sustainable material circulation. Here we develop a step toward the integrated simulation of energy-materials scenarios by unifying a stock-flow dynamics model for low-carbon scenarios using linear programming. The modeling framework incorporates lithium supply from both mines and end-of-life (EoL) recycling for projected use in electric vehicles on a global basis. The results show that supply constraints, which could become apparent from around 2030 in the case of current recycling rates (<1%), would impede the deployment of battery electric vehicles (BEVs), leading to the generation of an additional 300 Mt-CO₂ of emissions for vehicle operation in 2050. Another important finding is that increasing the recycling rate to 80% could substantially relieve restrictions on the introduction of BEVs without requiring primary supply from natural deposits far beyond historical rates of expansion. While EoL recycling is important from a long-term perspective, an EoL-oriented strategy has little effect on the short/medium-term (such as to 2030) lithium demand-supply balance because of exponential demand growth and long living batteries. Importantly, findings in this study emphasize the necessity of tackling climate change and resource circulation in an integrated manner.

Mapping the Annual Flow of Steel in the United States

A detailed understanding of material flows is needed to target increased material efficiency and circular economy. In this article, the U.S. steel flow is modeled as a series of nodes representing processes and products. An easily updatable nonlinear least squares optimization is used to reconcile the inconsistencies across 293 collated data records on flows through and between the nodes. The data come from an integrated analysis that includes top-down estimates of steel flow from trade bodies and government statistical agencies, bottom-up estimates of the steel embedded in products based on production statistics and bills of materials, and the mass of imports and exports based on international money flow. A weighting methodology is used to consistently assign confidence scores to the data, and the optimization is used to achieve mass balance and minimize the sum of the squares of the weighted residuals. The results indicate that yield improvement efforts should focus on sheet metal forming in the car industry, which accounts for nearly half of all generated fabrication scrap. The quantity of end-of-life scrap exported and land-filled is greater than the quantity of steel products imported. Increased domestic recycling of end-of-life scrap might displace around a third of these imports.

Taking Stock of Built Environment Stock Studies: Progress and Prospects

Built environment stocks (buildings and infrastructures) play multiple roles in our socio-economic metabolism: they serve as the backbone of modern societies and human well-being, drive the material cycles throughout the economy, entail temporal and spatial lock-ins on energy use and emissions, and represent an extensive reservoir of secondary materials. This review aims at providing a comprehensive and critical review of the state of the art, progress, and prospects of built environment stocks research which has boomed in the past decades. We included 249 publications published from 1985 to 2018, conducted a bibliometric analysis, and assessed the studies by key characteristics including typology of stocks (status of stock and end-use category), type of measurement (object and unit), spatial boundary and level of resolution, and temporal scope. We also highlighted the strengths and weaknesses of different estimation approaches. A comparability analysis of existing studies shows a clearly higher level of stocks per capita and per area in developed countries and cities, confirming the role of urbanization and industrialization in built environment stock growth. However, more spatially refined case studies (e.g., on developing cities and nonresidential buildings) and standardization and improvement of methodology (e.g., with geographic information system and architectural knowledge) and data (e.g., on material intensity and lifetime) would be urgently needed to reveal more robust conclusions on the patterns, drivers, and implications of built environment stocks. Such advanced knowledge on built environment stocks could foster societal and policy agendas such as urban sustainability, circular economy, climate change, and United Nations 2030 Sustainable Development Goals.

Integrating Dynamic Material Flow Analysis and Computable General Equilibrium Models for Both Mass and Monetary Balances in Prospective Modeling: A Case for the Chinese Building Sector

Integrated Assessment Models based on Computable General Equilibrium (IAM/CGE) and dynamic Material Flow Analysis (dynamic MFA) are two most widely used prospective model families to assess large-scale and long-term socioeconomic metabolism (SEM) and inform sustainable SEM transition. The latter approach could complement the former by a more explicit understanding of service provision, in-use stocks, and material cycles in a mass balanced framework. In this paper, we demonstrated this by integrating the dynamic MFA and CGE model approaches for the Chinese building sector from 2012 to 2030. Our results revealed the impacts of building stock dynamics on sectoral and economy-wide CO₂ emissions: lower service saturation levels and later saturation time of building stock development could free up investment on buildings and accumulatively save up to 25.4 Gt in embodied CO₂ emissions of the building construction sector, representing a 2.7-fold of 2012 countrywide CO₂ emissions. However, the save-ups are partly compensated by an increase of embodied CO₂ emissions in the other sectors due to economy-wide rebound effect (ca. 18.8 Gt or about 74%). The integrated model we developed could help ensure both mass and monetary balances, explore rebound effects in prospective modeling, and thus better understand the economy-wide consequences of infrastructure development.

Scenarios for Demand Growth of Metals in Electricity Generation Technologies, Cars, and Electronic Appliances

This study provides scenarios toward 2050 for the demand of five metals in electricity production, cars, and electronic appliances. The metals considered are copper, tantalum, neodymium, cobalt, and lithium. The study shows how highly technology-specific data on products and material flows can be used in integrated assessment models to assess global resource and metal demand. We use the Shared Socio-economic Pathways as implemented by the IMAGE integrated assessment model as a starting point. This allows us to translate information on the use of electronic appliances, cars, and renewable energy technologies into quantitative data on metal flows, through application of metal content estimates in combination with a dynamic stock model. Results show that total demand for copper, neodymium, and tantalum might increase by a factor of roughly 2 to 3.2, mostly as a result of population and GDP growth. The demand for lithium and cobalt is expected to increase much more, by a factor 10 to more than 20, as a result of future (hybrid) electric car purchases. This means that not just demographics, but also climate policies can strongly increase metal demand. This shows the importance of studying the issues of climate change and resource depletion together, in one modeling framework.

Resource Demand Scenarios for the Major Metals

The growth in metal use in the past few decades raises concern that supplies may be insufficient to meet demands in the future. From the perspective of historical and current use data for seven major metals-iron, manganese, aluminum, copper, nickel, zinc, and lead-we have generated several scenarios of potential metal demand from 2010 to 2050 under alternative patterns of global development. We have also compared those demands with various assessments of potential supply to midcentury. Five conclusions emerge: (1) The calculated demand for each of the seven metals doubles or triples relative to 2010 levels by midcentury; (2) The largest demand increases relate to a scenario in which increasingly equitable values and institutions prevail throughout the world; (3) The metal recycling flows in the scenarios meet only a modest fraction of future metals demand for the next few decades; (4) In the case of copper, zinc, and perhaps lead, supply may be unlikely to meet demand by about midcentury under the current use patterns of the respective metals; (5) Increased rates of demand for metals imply substantial new energy provisioning, leading to increases in overall global energy demand of 21-37%. These results imply that extensive technological transformations and governmental initiatives could be needed over the next several decades in order that regional and global development and associated metal demand are not to be constrained by limited metal supply.

Calculation of Characterization Factors of Mineral Resources Considering Future Primary Resource Use Changes: A Comparison between Iron and Copper

The future availability of mineral resources has attracted much attention; therefore, a quantitative evaluation of the potential impacts of resource use on future availability is important. Although the surplus cost model is often recommended among the existing endpoint characterization models of mineral resources, it has a shortcoming as it does not consider the changes in future primary resource use. This paper introduces a new characterization model considering future primary resource use changes, due to future changes in total demand and secondary resource use. Using material flow analysis, this study estimated time-series primary resource use for iron and copper for five shared socioeconomic pathways (SSPs) and a constant total demand scenario. New characterization factors, i.e., demand change-based surplus costs (DCSC), are calculated for each resource. In all of the SSPs, the calculated DCSCs are larger than the conventional surplus costs (SC) for both iron and copper. The DCSC, relative to the SC of copper, is larger than that of iron for all of the SSPs, which suggests that the potential impacts of copper use, relative to iron, will be underestimated, unless future primary resource use changes are considered. In calculating DCSC for other resources, it is important to choose an appropriate approach for forecasting future total demands.

Dynamic Model for the Stocks and Release Flows of Engineered Nanomaterials

Most existing life-cycle release models for engineered nanomaterials (ENM) are static, ignoring the dynamics of stock and flows of ENMs. Our model, nanoRelease, estimates the annual releases of ENMs from manufacturing, use, and disposal of a product explicitly taking stock and flow dynamics into account. Given the variabilities in key parameters (e.g., service life of products and annual release rate during use) nanoRelease is designed as a stochastic model. We apply nanoRelease to three ENMs (TiO₂, SiO₂ and FeO_x) used in paints and coatings through seven product applications, including construction and building, household and furniture, and automotive for the period from 2000 to 2020 using production volume and market projection information. We also consider model uncertainties using Monte Carlo simulation. Compared with 2016, the total annual releases of ENMs in 2020 will increase by 34-40%, and the stock will increase by 28-34%. The fraction of the end-of-life release among total release flows will increase from 11% in 2002 to 43% in 2020. As compared to static models, our dynamic model predicts about an order of magnitude lower values for the amount of ENM released from this sector in the near-term while stock continues to build up in the system.

Elaborating the History of Our Cementing Societies: An in-Use Stock Perspective

Modern cities and societies are built fundamentally based on cement and concrete. The global cement production has risen sharply in the past decades due largely to urbanization and construction. Here we deployed a top-down dynamic material flow analysis (MFA) model to quantify the historical development of cement in-use stocks in residential, nonresidential, and civil engineering sectors of all world countries. We found that global cement production spreads unevenly among 184 countries, with China dominating the global production and consumption after the 1990s. Nearly all countries have shown an increasing trend of per capita cement in-use stock in the past century. The present per capita cement in-use stocks vary from 10 to 40 tonnes in major industrialized and transiting countries and are below 10 tonnes in developing countries. Evolutionary modes identified from historical patterns suggest that per capita in-use cement stock growth generally complies with an S-shape curve and relates closely to affluence and urbanization of a country, but more in-depth and bottom-up investigations are needed to better understand socioeconomic drivers behind stock growth. These identified in-use stock patterns can help us better estimate future demand of cement, explore strategies for emissions reduction in the cement industry, and inform CO₂ uptake potentials of cement based products and infrastructure in service.

Quantifying Recycling and Losses of Cr and Ni in Steel Throughout Multiple Life Cycles Using MaTrace-Alloy

Alloying metals are indispensable ingredients of high quality alloy steel such as austenitic stainless steel, the cyclical use of which is vital for sustainable resource management. Under the current practice of recycling, however, different metals are likely to be mixed in an uncontrolled manner, resulting in function losses and dissipation of metals with distinctive functions, and in the contamination of recycled steels. The latter could result in dilution loss, if metal scrap needed dilution with virgin iron to reduce the contamination below critical levels. Management of these losses resulting from mixing in repeated recycling of metals requires tracking of metals over multiple life cycles of products with compositional details. A new model (MaTrace-alloy) was developed that tracks the fate of metals embodied in each of products over multiple life cycles of products, involving accumulation, discard, and recycling, with compositional details at the level of both alloys and products. The model was implemented for the flow of Cr and Ni in the Japanese steel cycle involving 27 steel species and 115 final products. It was found that, under a high level of scrap sorting, greater than 70% of the initial functionality of Cr and Ni could be retained over a period of 100 years, whereas under a poor level of sorting, it could plunge to less than 30%, demonstrating the relevance of waste management technology in circular economy policies.

How Will Copper Contamination Constrain Future Global Steel Recycling?

Copper in steel causes metallurgical problems, but is pervasive in end-of-life scrap and cannot currently be removed commercially once in the melt. Contamination can be managed to an extent by globally trading scrap for use in tolerant applications and dilution with primary iron sources. However, the viability of long-term strategies can only be evaluated with a complete characterization of copper in the global steel system and this is presented in this paper. The copper concentration of flows along the 2008 steel supply chain is estimated from a survey of literature data and compared with estimates of the maximum concentration that can be tolerated in steel products. Estimates of final steel demand and scrap supply by sector are taken from a global stock-saturation model to determine when the amount of copper in the steel cycle will exceed that which can be tolerated. Best estimates show that quantities of copper arising from conventional scrap preparation can be managed in the global steel system until 2050 assuming perfectly coordinated trade and extensive dilution, but this strategy will become increasingly impractical. Technical and policy interventions along the supply chain are presented to close product loops before this global constraint.

End-of-Life in the railway sector: Analysis of recyclability and recoverability for different vehicle case studies

The railway system represents one of the most resource-efficient answer to our ever-growing demand for transport service and the development trends for the following years forecast a substantial increase in this sector. Considering the European Union, rolling stock realizes a significant share of both goods and passengers carriage while it is responsible for a derisory quota of environmental impact and energy consumption involved by transportation. Contrary to the low environmental impact, the amount of End-of-Life (EoL) waste generated by rolling stocks in relation to the number of vehicles is notable, much greater than in the case of road vehicles. As railway vehicles are constituted by many heterogeneous components, the EoL rolling stock is a precious source of materials, whose recycling brings measurable economic benefits and needs to be appropriately debated. The paper presents calculation of recoverability/recyclability rate for different typologies of vehicles representative of railway transport; calculation is performed on the basis of primary data and according to the recyclability and recoverability calculation method issued by UNIFE in the context of Product Category Rules (PCR). The typologies of railway vehicles taken into account are electric metro, diesel commuter train and high-speed electric train. The analysis envisages also to replicate the calculation in case innovative materials and manufacturing technologies are adopted in the construction of car-body structure. Results show that recyclability/recoverability rates are abundantly over the quota of 90% for each one of the three trains, these latter being made in major part of metals that benefit from very efficient recovery processes. The adoption of innovative materials and manufacturing technologies for car-body structure involves a scarce reduction of recyclability and recoverability rates (about 2% and 0.2% respectively) due to the introduction of components and materials characterized by critical dismantlability and low efficiency recovery processes; recoverability results less affected by lightweighting because post-shredding thermal recovery treatments are roughly independent with respect to dismantlability. A sensitivity analysis based on different dismantling scenarios reveals that the effectiveness of dismantling has a moderate influence on recyclability/recoverability rate (the variation does not exceed 3%). The low variability of recyclability/recoverability rate can be explained by the following reasons: predominance of metals in trains material composition, efficiency of metals separation processes close to 100%, post-shredding recycling processes of metals characterized by recovery factors equal to the ones of post-dismantling recycling processes.

Regional distribution and losses of end-of-life steel throughout multiple product life cycles-Insights from the global multiregional MaTrace model

Substantial amounts of post-consumer scrap are exported to other regions or lost during recovery and remelting, and both export and losses pose a constraint to desires for having regionally closed material cycles. To quantify the challenges and trade-offs associated with closed-loop metal recycling, we looked at the material cycles from the perspective of a single material unit and trace a unit of material through several product life cycles. Focusing on steel, we used current process parameters, loss rates, and trade patterns of the steel cycle to study how steel that was originally contained in high quality applications such as machinery or vehicles with stringent purity requirements gets subsequently distributed across different regions and product groups such as building and construction with less stringent purity requirements. We applied MaTrace Global, a supply-driven multiregional model of steel flows coupled to a dynamic stock model of steel use. We found that, depending on region and product group, up to 95% of the steel consumed today will leave the use phase of that region until 2100, and that up to 50% can get lost in obsolete stocks, landfills, or slag piles until 2100. The high losses resulting from business-as-usual scrap recovery and recycling can be reduced, both by diverting postconsumer scrap into long-lived applications such as buildings and by improving the recovery rates in the waste management and remelting industries. Because the lifetimes of high-quality (cold-rolled) steel applications are shorter and remelting occurs more often than for buildings and infrastructure, we found and quantified a tradeoff between low losses and high-quality applications in the steel cycle. Furthermore, we found that with current trade patterns, reduced overall losses will lead to higher fractions of secondary steel being exported to other regions. Current loss rates, product lifetimes, and trade patterns impede the closure of the steel cycle.

Stochastic Analysis and Forecasts of the Patterns of Speed, Acceleration, and Levels of Material Stock Accumulation in Society

The recent acceleration of urbanization and industrialization of many parts of the developing world, most notably in Asia, has resulted in a fast-increasing demand for and accumulation of construction materials in society. Despite the importance of physical stocks in society, the empirical assessment of total material stock of buildings and infrastructure and reasons for its growth have been underexplored in the sustainability literature. We propose an innovative approach for explaining material stock dynamics in society and create a country typology for stock accumulation trajectories using the ARIMA (Autoregressive Integrated Moving Average) methodology, a stochastic approach commonly used in business studies and economics to inspect and forecast time series. This enables us to create scenarios for future demand and accumulation of building materials in society, including uncertainty estimates. We find that the so-far overlooked aspect of acceleration trends of material stock accumulation holds the key to explaining material stock growth, and that despite tremendous variability in country characteristics, stock accumulation is limited to only four archetypal growth patterns. The ability of nations to change their pattern will be a determining factor for global sustainability.

Macroscopic Evidence for the Hibernating Behavior of Materials Stock

Hibernating stock is defined as material stock that is no longer used, but is not yet recovered. Although hibernating stock plays a role in materials recoverability, its contribution to the overall material cycle is not clearly understood. Therefore, an analysis of the time-series potential generation of steel scrap in Japan was performed and compared against the actual recovery, proving that the steel scrap recovered each year exceeds the annual generation potential and providing the first macroscopic evidence of hibernating stock recovery. These results indicate that hibernation behavior should be considered when evaluating materials recoverability. The particular characteristics of hibernating stock were also identified. These materials tend to be located far from scrap yards and/or have low bulk density, while also minimally obstructing new activity. In fact, hibernating materials are typically only recovered when they obstruct new activity. Hence, in order to increase steel recoverability, the recovery cost must be reduced. The end-of-life recycling rates (EoL-RRs) were also evaluated, and were found to exhibit a significant change over time. Consequently, the annual EoL-RR cannot be considered as a representative value, and a value for the EoL-RR(s) of relevant year(s) that has been evaluated over the entire period should be used instead.

MaTrace: tracing the fate of materials over time and across products in open-loop recycling

Even for metals, open-loop recycling is more common than closed-loop recycling due, among other factors, to the degradation of quality in the end-of-life (EoL) phase. Open-loop recycling is subject to loss of functionality of original materials, dissipation in forms that are difficult to recover, and recovered metals might need dilution with primary metals to meet quality requirements. Sustainable management of metal resources calls for the minimization of these losses. Imperative to this is quantitative tracking of the fate of materials across different stages, products, and losses. A new input-output analysis (IO) based model of dynamic material flow analysis (MFA) is presented that can trace the fate of materials over time and across products in open-loop recycling taking explicit consideration of losses and the quality of scrap into account. Application to car steel recovered from EoL vehicles (ELV) showed that after 50 years around 80% of the steel is used in products, mostly buildings and civil engineering (infrastructure), with the rest mostly resided in unrecovered obsolete infrastructure and refinery losses. Sensitivity analysis was conducted to evaluate the effects of changes in product lifespan, and the quality of scrap.

Modeling metal stocks and flows: a review of dynamic material flow analysis methods

Dynamic material flow analysis (MFA) is a frequently used method to assess past, present, and future stocks and flows of metals in the anthroposphere. Over the past fifteen years, dynamic MFA has contributed to increased knowledge about the quantities, qualities, and locations of metal-containing goods. This article presents a literature review of the methodologies applied in 60 dynamic MFAs of metals. The review is based on a standardized model description format, the ODD (overview, design concepts, details) protocol. We focus on giving a comprehensive overview of modeling approaches and structure them according to essential aspects, such as their treatment of material dissipation, spatial dimension of flows, or data uncertainty. The reviewed literature features similar basic modeling principles but very diverse extrapolation methods. Basic principles include the calculation of outflows of the in-use stock based on inflow or stock data and a lifetime distribution function. For extrapolating stocks and flows, authors apply constant, linear, exponential, and logistic models or approaches based on socioeconomic variables, such as regression models or the intensity-of-use hypothesis. The consideration and treatment of further aspects, such as dissipation, spatial distribution, and data uncertainty, vary significantly and highly depends on the objectives of each study.

Past and future cadmium emissions from municipal solid-waste incinerators in Japan for the assessment of cadmium control policy

Cadmium (Cd) is a harmful pollutant emitted from municipal solid-waste incinerators (MSWIs). Cd stack emissions from MSWIs have been estimated between 1970 and 2030 in Japan. The aims of this study are to quantify emitted Cd by category and to analyze Cd control policies to reduce emissions. Emissions were estimated using a dynamic substance flow analysis (SFA) that took into account representative waste treatment flows and historical changes in emission factors. This work revealed that the emissions peaked in 1973 (11.1t) and were ten times those in 2010 (1.2 t). Emission from MSWIs was two-thirds of that from non-ferrous smelting in 2010. The main Cd emission source was pigment use in the 1970s, but after 2000 it had shifted to nickel-cadmium (Ni-Cd) batteries. Future emissions were estimated for 2030. Compared to the business-as-usual scenario, an intensive collection of used Ni-Cd batteries and a ban on any future use of Ni-Cd batteries will reduce emissions by 0.09 and 0.3 1t, respectively, in 2030. This approach enables us to identify the major Cd emission source from MSWIs, and to prioritize the possible Cd control policies.

Towards a dynamic assessment of raw materials criticality: linking agent-based demand--with material flow supply modelling approaches

Emerging technologies such as information and communication-, photovoltaic- or battery technologies are expected to increase significantly the demand for scarce metals in the near future. The recently developed methods to evaluate the criticality of mineral raw materials typically provide a 'snapshot' of the criticality of a certain material at one point in time by using static indicators both for supply risk and for the impacts of supply restrictions. While allowing for insights into the mechanisms behind the criticality of raw materials, these methods cannot account for dynamic changes in products and/or activities over time. In this paper we propose a conceptual framework intended to overcome these limitations by including the dynamic interactions between different possible demand and supply configurations. The framework integrates an agent-based behaviour model, where demand emerges from individual agent decisions and interaction, into a dynamic material flow model, representing the materials' stocks and flows. Within the framework, the environmental implications of substitution decisions are evaluated by applying life-cycle assessment methodology. The approach makes a first step towards a dynamic criticality assessment and will enhance the understanding of industrial substitution decisions and environmental implications related to critical metals. We discuss the potential and limitation of such an approach in contrast to state-of-the-art methods and how it might lead to criticality assessments tailored to the specific circumstances of single industrial sectors or individual companies.

Simultaneous material flow analysis of nickel, chromium, and molybdenum used in alloy steel by means of input-output analysis

Steel is not elemental iron but rather a group of iron-based alloys containing many elements, especially chromium, nickel, and molybdenum. Steel recycling is expected to promote efficient resource use. However, open-loop recycling of steel could result in quality loss of nickel and molybdenum and/or material loss of chromium. Knowledge about alloying element substance flow is needed to avoid such losses. Material flow analyses (MFAs) indicate the importance of steel recycling to recovery of alloying elements. Flows of nickel, chromium, and molybdenum are interconnected, but MFAs have paid little attention to the interconnected flow of materials/substances in supply chains. This study combined a waste input-output material flow model and physical unit input-output analysis to perform a simultaneous MFA for nickel, chromium, and molybdenum in the Japanese economy in 2000. Results indicated the importance of recovery of these elements in recycling policies for end-of-life (EoL) vehicles and constructions. Improvement in EoL sorting technologies and implementation of designs for recycling/disassembly at the manufacturing phase are needed. Possible solutions include development of sorting processes for steel scrap and introduction of easier methods for identifying the composition of secondary resources. Recovery of steel scrap with a high alloy content will reduce primary inputs of alloying elements and contribute to more efficient resource use.

The roles of energy and material efficiency in meeting steel industry CO2 targets

Identifying strategies for reducing greenhouse gas emissions from steel production requires a comprehensive model of the sector but previous work has either failed to consider the whole supply chain or considered only a subset of possible abatement options. In this work, a global mass flow analysis is combined with process emissions intensities to allow forecasts of future steel sector emissions under all abatement options. Scenario analysis shows that global capacity for primary steel production is already near to a peak and that if sectoral emissions are to be reduced by 50% by 2050, the last required blast furnace will be built by 2020. Emissions reduction targets cannot be met by energy and emissions efficiency alone, but deploying material efficiency provides sufficient extra abatement potential.

The steel scrap age

Steel production accounts for 25% of industrial carbon emissions. Long-term forecasts of steel demand and scrap supply are needed to develop strategies for how the steel industry could respond to industrialization and urbanization in the developing world while simultaneously reducing its environmental impact, and in particular, its carbon footprint. We developed a dynamic stock model to estimate future final demand for steel and the available scrap for 10 world regions. Based on evidence from developed countries, we assumed that per capita in-use stocks will saturate eventually. We determined the response of the entire steel cycle to stock saturation, in particular the future split between primary and secondary steel production. During the 21st century, steel demand may peak in the developed world, China, the Middle East, Latin America, and India. As China completes its industrialization, global primary steel production may peak between 2020 and 2030 and decline thereafter. We developed a capacity model to show how extensive trade of finished steel could prolong the lifetime of the Chinese steelmaking assets. Secondary steel production will more than double by 2050, and it may surpass primary production between 2050 and 2060: the late 21st century can become the steel scrap age.

Transitions to material efficiency in the UK steel economy

Steel production is energy intensive so already has achieved impressive levels of energy efficiency. If the emissions associated with steel must be reduced in line with the requirements of the UK Climate Change Act, demand for new steel must be reduced. The strategies of 'material efficiency' aim to achieve such a reduction, while delivering the same final services. To meet the emissions targets set into UK law, UK consumption of steel must be reduced to 30 per cent of present levels by 2050. Previous work has revealed six strategies that could contribute to this target, and this paper presents an approximate analysis of the required transition. A macro-economic analysis of steel in the UK shows that while the steel industry is relatively small, the construction and manufacturing sectors are large, and it would be politically unacceptable to pursue options that lead to a major contraction in other sectors. Alternative business models are therefore required, and these are explored through four representative products--one for each final sector with particular emphasis given to options for reducing product weight, and extending product life. Preliminary evidence on the triggers that would lead to customers preferring these options is presented and organized in order to predict required policy measures. The estimated analysis of transitions explored in this paper is used to define target questions for future research in the area.

Product life trade-offs: what if products fail early?

Increasing product life allows the embodied emissions in products to be spread across a longer period but can mean that opportunities to improve use-phase efficiency are foregone. In this paper, a model that evaluates this trade-off is presented and used to estimate the optimal product life for a range of metal-intensive products. Two strategies that have potential to save emissions are explored: (1) adding extra embodied emissions to make products more sturdy, increasing product life, and (2) increasing frequency of use, causing early product failure to take advantage of improvements in use-phase efficiency. These strategies are evaluated for two specific case studies (long-life washing machines and more frequent use of vehicles through car clubs) and for a range of embodied and use-phase intensive products under different use-phase improvement rate assumptions. Particular emphasis is placed on the fact that products often fail neither at their design life nor at their optimal life. Policy recommendations are then made regarding the targeting of these strategies according to product characteristics and the timing of typical product failure relative to optimal product life.

Mapping the global flow of steel: from steelmaking to end-use goods

Our society is addicted to steel. Global demand for steel has risen to 1.4 billion tonnes a year and is set to at least double by 2050, while the steel industry generates nearly a 10th of the world's energy related CO₂ emissions. Meeting our 2050 climate change targets would require a 75% reduction in CO₂ emissions for every tonne of steel produced and finding credible solutions is proving a challenge. The starting point for understanding the environmental impacts of steel production is to accurately map the global steel supply chain and identify the biggest steel flows where actions can be directed to deliver the largest impact. In this paper we present a map of global steel, which for the first time traces steel flows from steelmaking, through casting, forming, and rolling, to the fabrication of final goods. The diagram reveals the relative scale of steel flows and shows where efforts to improve energy and material efficiency should be focused.

Reusing steel and aluminum components at end of product life

Reusing steel and aluminum components would reduce the need for new production, possibly creating significant savings in carbon emissions. Currently, there is no clearly defined set of strategies or barriers to enable assessment of appropriate component reuse; neither is it possible to predict future levels of reuse. This work presents a global assessment of the potential for reusing steel and aluminum components. A combination of top-down and bottom-up analyses is used to allocate the final destinations of current global steel and aluminum production to product types. A substantial catalogue has been compiled for these products characterizing key features of steel and aluminum components including design specifications, requirements in use, and current reuse patterns. To estimate the fraction of end-of-life metal components that could be reused for each product, the catalogue formed the basis of a set of semistructured interviews with industrial experts. The results suggest that approximately 30% of steel and aluminum used in current products could be reused. Barriers against reuse are examined, prompting recommendations for redesign that would facilitate future reuse.

Anthropogenic cycles of the elements: a critical review

A cycle is the quantitative characterization of the flows of a specific material into, within, and from a given system. An anthropogenic elemental cycle can be static (for a point in time) or dynamic (over a time interval). The about 350 publications collected for this review contain a total of 1074 individual cycle determinations, 989 static and 85 dynamic, for 59 elements; more than 90% of the publications have appeared since 2000. The cycles are of varying quality and completeness, with about 80% at country- or territory-level, addressing 45 elements, and 5% at global-level, addressing 30 elements. Despite their limitations, cycles have often been successful in revealing otherwise unknown information. Most of the elements for which no cycles exist are radioactively unstable or are used rarely and in small amounts. For a variety of reasons, the anthropogenic cycles of only perhaps a dozen elements are well characterized. For all the others, with cycles limited or nonexistent, our knowledge of types of uses, lifetimes in those uses, international trade, losses to the environment, and rates of recycling is quite limited, thereby making attempts to evaluate resource sustainability particularly problematic.

Moving toward the circular economy: the role of stocks in the Chinese steel cycle

As the world's largest CO(2) emitter and steel producer, China has set the ambitious goal of establishing a circular economy which aims at reconciling economic development with environmental protection and sustainable resource use. This work applies dynamic material flow analysis to forecast production, recycling, and iron ore consumption in the Chinese steel cycle until 2100 by using steel services in terms of in-use stock per capita as driver of future development. The whole cycle is modeled to determine possible responses of the steel industry in light of the circular economy concept. If per-capita stock saturates at 8-12 tons as evidence from industrialized countries suggests, consumption may peak between 2015 and 2020, whereupon it is likely to drop by up to 40% until 2050. A slower growing in-use stock could mitigate this peak and hence reduce overcapacity in primary production. Old scrap supply will increase substantially and it could replace up to 80% of iron ore as resource for steel making by 2050. This would require advanced recycling technologies as manufacturers of machinery and transportation equipment would have to shift to secondary steel as well as new capacities in secondary production which could, however, make redundant already existing integrated steel plants.

Patterns of iron use in societal evolution

A dynamic material flow model was used to analyze the patterns of iron stocks in use for six industrialized countries. The contemporary iron stock in the remaining countries was estimated assuming that they follow a similar pattern of iron stock per economic activity. Iron stocks have reached a plateau of about 8-12 tons per capita in the United States, France, and the United Kingdom, but not yet in Japan, Canada, and Australia. The global average iron stock was determined to be 2.7 tons per capita. An increase to a level of 10 tons over the next decades would deplete about the currently identified reserves. A subsequent saturation would open a long-term potential to dramatically shift resource use from primary to secondary sources. The observed saturation pattern implies that developing countries with rapidly growing stocks have a lower potential for recycling domestic scrap and hence for greenhouse gas emissions saving than industrialized countries, a fact that has not been addressed sufficiently in the climate change debate.